An example of an all-wheel transmission system is disclosed in U.S. Pat. No. 4,709,775 and referred to as a so-called distributor transmission. Specifically, this distributor transmission includes two multi-plate friction clutches that are accommodated in a common housing which also acts as a clutch component for both friction clutches. The friction clutches are hydraulically actuated so that the torque transmitted can be controlled by modulating the fluid pressure.
In such torque distributor transmissions, operational safety makes it necessary for the friction clutches to automatically adopt a safe position in the event of a system failure, and yet be sufficiently engaged when the vehicle is parked to maintain a locking torque. Operational safety in a larger sense also includes the ability to provide a limp-home mode which permits the vehicle to be driven to a repair shop in the event of a system failure.